I have this code using c#.

public partial class MainForm : Form
{

    private CvCapture VideoCapture;

    private IplImage frame;
    private IplImage imgMain;

    public MainForm()
    {
        InitializeComponent();
    }



    private void btnVideo_Click(object sender, EventArgs e)
    {
        double vidWidth, vidHeight;

        try
        {
            VideoCapture = highgui.CvCreateCameraCapture(0);
        }
        catch (Exception except)
        {
            MessageBox.Show(except.Message);
        }

        if (btnVideo.Text.CompareTo("Start Video") == 0)
        {

            if (VideoCapture.ptr == IntPtr.Zero)
            {
                MessageBox.Show("badtrip ah!!!");
                return;
            }

            btnVideo.Text = "Stop Video";

            highgui.CvSetCaptureProperty(ref VideoCapture, highgui.CV_CAP_PROP_FRAME_WIDTH, 640);
            highgui.CvSetCaptureProperty(ref VideoCapture, highgui.CV_CAP_PROP_FRAME_HEIGHT, 480);

            highgui.CvQueryFrame(ref VideoCapture);

            vidWidth = highgui.cvGetCaptureProperty(VideoCapture, highgui.CV_CAP_PROP_FRAME_WIDTH);
            vidHeight = highgui.cvGetCaptureProperty(VideoCapture, highgui.CV_CAP_PROP_FRAME_HEIGHT);

            picBoxMain.Width = (int)vidWidth;
            picBoxMain.Height = (int)vidHeight;


            timerGrab.Enabled = true;
            timerGrab.Interval = 42;
            timerGrab.Start();

        }

        else
        {
            btnVideo.Text = "Start Video";
            timerGrab.Enabled = false;

            if (VideoCapture.ptr == IntPtr.Zero)
            {
                highgui.CvReleaseCapture(ref VideoCapture);
                VideoCapture.ptr = IntPtr.Zero;
            }
        }
    }

    private void timerGrab_Tick(object sender, EventArgs e)
    {
        try
        {
            frame = highgui.CvQueryFrame(ref VideoCapture);

            if (frame.ptr == IntPtr.Zero)
            {
                timerGrab.Stop();
                MessageBox.Show("??");
                return;
            }

            imgMain = cxcore.CvCreateImage(cxcore.CvGetSize(ref frame), 8, 3);

            picBoxMain.Image = highgui.ToBitmap(imgMain, false);

            cxcore.CvReleaseImage(ref imgMain);
            //cxcore.CvReleaseImage(ref frame);
        }
        catch (Exception excpt)
        {
            MessageBox.Show(excpt.Message);
        }
    }
}

The problem is after i break all and step through the debugger the program stops at a certain code.

the code where it stops is here: frame = highgui.CvQueryFrame(ref VideoCapture); the error is that it says that cannot evaluate expression because a native frame is on top of the call stack.

and then when i try to shift+F11 it. there is another error saying that system.accessviolationexception.

the stack trace says that: at System.Runtime.InteropServices.Marshal.CopyToManaged(IntPtr source, Object destination, Int32 startIndex, Int32 length) at CxCore.IplImage.get_ImageDataDb()